Usually, underground etc., many metal tubes, such as a gas pipe, a water pipe, and a drain pipe, or many cables, such as a telecommunication cable and an electric power cable, are buried.
In pillars and walls of a structure, such as a building, many buried metals are buried.
(Hereafter, except for a conventional example portion, these are named only described as a buried metal. Underground and structure are only described as underground.)
These buried metals are not buried in the shape of a straight line horizontally or vertically, since these buried metals are crooked horizontally or vertically or are branched, these buried metals cross intricately, and are constructed by congestion.
Thus, since many buried metals are constructed underground, for the accident prevention by construction of other companies, and the efficient control of maintenance of the buried metal of its company, the art for detecting the position and its burial depth of a buried metal without excavating is proposed.
As general prior art, there are an underground radar and an electromagnetic guidance pipeline detector so-called a pipe locator.
The detection principle of the underground radar which detects the metal tube currently buried in the ground is as follows.
An electric wave is emitted in the ground and the reflective wave from the metal tube currently buried in the ground is received, and signal processing of this received signal is carried out, it converts into a video signal, and a metal tube is detected.
Since an electric wave is reflected from the face where an electrical characteristic changes, underground structure such as a metal tube, a nonmetallic pipe, and a cave can also be detected by this method.
As a conventional example of the pipe locator by an electromagnetic induction method, there is an electromagnetic guidance pipeline detector (common name: a pipe locator) shown in non-patent document 1.
The detection principle of this pipe locator is as follows.
As shown in FIGS. 5(a)-(c), if an alternating current is passed through metal tubes 51 currently buried underground 50, the magnetic field (magnetic field H) of the shape of a concentric circle centering on this metal tube 51 will occur (refer to FIG. 5(b)).
This magnetic field H is detected with magnetic sensor 52a of the receiver which is on the ground, and this magnetic field H is calculated, and induction voltage is calculated.
The position of metal tube 51 can be detected from the position where this induction voltage becomes the maximum (refer to FIG. 5(c)).
The burial depth of metal tube 51 is calculated from this induction voltage.
Therefore, target for detection is limited to the metal tube or metal line which has conductivity.
Thus, the pipe locator is constituted by the transmitter 53 for sending current through metal tube 51 and the receiver provided with magnetic sensor 52a which detects magnetic field H generated when current flowed.
There are two kinds of methods of sending current through metal tube 51 from transmitter 53, direct method and an induction method.
As shown in FIG. 6, in the direct method, transmitter 53 is connected to metal tube 51 portion exposed on the ground, or transmitter 53 is connected to metal tubes 51 buried underground 50 via lead 54, and current is passed.
The leak current which flows into underground 50 from metal tube 51 is constituted so that it may feedback to transmitter 53 via earth 55.
As shown in FIG. 7, in the induction method, an electric wave is emitted towards underground 50 from transmitter 53a installed on the ground, and a magnetic field is generated.
Therefore, transmitter 53a and metal tube 51 of underground 50 becomes non-contact mutually, and the current (induced current) by electromagnetic induction flows into metal tube 51.
The magnetic field generated by the induced current receives with the ground receiver provided with magnetic sensor 52a, and is detecting a position and burial depth, etc. of metal tube 51 of underground from the amplitude of the magnetic field component of this magnetic field.
As shown in FIG. 6, in the direct method, since an alternating current can be passed only through metal tube 51 which is a target for detection, the value of magnetic field H to generate also becomes large, and detection accuracy is good compared with the induction method.
However, in the direct method, since transmitter 53 must be directly connected to metal tube 51, it is hard to apply to the metal tube which does not have an exposed portion on the ground.
In the above-mentioned electromagnetic induction type exploration equipment (pipe locator), the frequency of the alternating current (transmitting signal) for detection changes with the kinds and the burial conditions of a burial material.
For example, in the case of the cable, generally, the frequency of hundreds of Hz-several kHz is used, and, in the case of the gas pipe, the water pipe, etc., the frequency of tens of kHz-hundreds of kHz is used.
Moreover, if the transmitting signal for detection is emitted to the underground pipe which is the target for detection, although induced current flows into other pipes (pipe of a congestion state) buried under the neighborhood by the alternating current which flows into an underground pipe, the direction of induced current which flows into the underground pipe of target for detection and other pipes is opposite.
Therefore, in order to judge whether the underground pipe of target for detection is tracked correctly, it is effective to grasp the information about the direction of induced current.
For example, as shown in FIG. 8, when the gas pipe 60 and the water pipe 61 are buried in the state of congestion and both pipes are connected with hot-water supply machine 62, the direction of the alternating current for detection which is inputted from transmitter 63 and flows into a gas pipe and the direction of the alternating current for detection which flows into a water pipe is opposite direction mutually.
Therefore, if the direction of the alternating current which flows into gas pipe 60 and the direction of an alternating current which flows into water pipe 61 are known, it can judge which pipe is target for detection.
As a method of distinguishing the direction of current which flows into the target for detection, there are a method of using CD wave (Current Flow Direction) as a signal for detection, and a method of using synchronous detection.
As shown in non-patent document 2, as a method of using CD wave, there is continuous underground burial material detecting art by an electromagnetic induction method.
This art consists of Cable Explorer (brand name) 73 which can check the position of an underground burial material continuously by earth surface to un-excavating, and an oscillator 72 which oscillates a signal required for measurement.
As shown in FIG. 9 and FIG. 10, when measuring the position of the underground burial material 71 buried underground 70, the position information on underground burial material 71 is continuously acquirable by three dimensions by interlocking underground burial material detecting device 75 which measures the burial depth of underground burial material 71, and RTK-GPS74 which can acquire position information.
In underground burial material detecting device 75, oscillator 72 is directly connected to underground burial material 71, the magnetic field generated by sending current through underground burial material 71 is detected on the ground, and the burial depth of underground burial material 71 is measured.
In RTK-GPS (Real Time Kinematic Global Positioning System) 74, position information is acquired using GPS74a, GPS74b, and GPS74c . . . which is highly precise and can acquire the plane position information (latitude, longitude) of underground burial material 71.
Cable Explorer 73 is constituted by the underground burial material exploration equipment 75, GPS-RKT74 which obtains the position information of truck, the optical gyroscope 76 which calculates the move direction of the truck, the odometer 77 which calculates the moving distance of the truck and personal computer ((hereafter PC) 78 which stores and processes the information that each equipment obtains.
These devices are laid on the cart which has a move function.
In addition, 79 is an indicator which shows a measurement result etc.
The underground burial material detecting device 75 receives the magnetic field generated by the alternating current which flows into the underground burial material 71, and is calculating position information by this magnetic field strength.
Plane position information is shown from the cart center by “+” or “−” in a horizontal direction toward the moving direction of underground burial material 71.
As for depth information, the distance from the earth surface to the center of the underground burial material 71 is shown.
On the other hand, as a method of using synchronous detection, there is an one-point method as indicated to patent documents 1.
As shown in FIG. 11 of the patent documents 1, by using the locator which has an oscillator 80, a receiver 81 and the ground means 82, by an one-point method, the exposed portion of underground pipes 83 which have conductivity and ground means 82 are connected to the output of oscillator 80 with an underground pipe which has conductivity or a locating wire etc., and the ground is made into a feedback line and the closed circuit which has a distribution constant circuit in part is constituted.
By scanning or operating it, detector 84 connected to receiver 81 detects the magnetic field guided by the current which flows into underground pipe 83, and is detecting underground pipe 83.
By this method, a phase detection means 86 to detect a phase is further prepared in the receiver 81 which has a detector 84 and the display means 85, and receiving information is obtained by this phase detection means 86, and position P1 of corresponding to the ground of underground pipe 83 and burial depth D is calculating based on this receiving information.